Thermo-osmosis in charged nanochannels: effects of surface charge and ionic strength

Abstract

Thermo-osmosis refers to fluid migration due to temperature gradient. The mechanistic understanding of thermo-osmosis in charged nano-porous media is still incomplete, while it is important for several environmental and energy applications, such as low-grade waste heat recovery, wastewater recovery, fuel cells, and nuclear waste storage. This paper presents results from a series of molecular dynamics simulations of thermo-osmosis in charged silica nanochannels that advance the understanding of the phenomenon. Simulations with pure water and water with dissolved NaCl are considered. First, the effect of surface charge on the sign and magnitude of the thermo-osmotic coefficient is quantified. This effect was found to be mainly linked to the structural modifications of aqueous electrical double layer (EDL) caused by the nanoconfinement and surface charges. In addition, the results illustrate that the surface charges reduce the self-diffusivity and thermo-osmosis of interfacial liquid. The thermo-osmosis was found to change direction when the surface charge density exceeds $-0.03C/m^2$. It was found that the thermo-osmotic flow and self-diffusivity increases with the concentration of NaCl. The fluxes of solvent and solute are decoupled by considering the Ludwig-Soret effect of NaCl ions to identify the main mechanisms controlling the behavior. In addition to the advance in microscopic quantification and mechanistic understanding of thermo-osmosis, the work provides approaches to investigate a broader category of coupled heat and mass transfer problems in nanoscale space.

32 pages, 11 figures

References in corpus (8)

• Canonical sampling through velocity-rescaling
• The Electrostatic Screening Length in Concentrated Electrolytes Increases with Concentration
• Liquid friction on charged surfaces: from hydrodynamic slippage to electrokinetics
• What controls thermo-osmosis? Molecular simulations show the critical role of interfacial hydrodynamics
• Ion specificity and anomalous electrokinetic effects in hydrophobic nanochannels
• Diffusion coefficient and shear viscosity of rigid water models
• Ion exchange in atomically thin clays and micas
• Thermal diffusion of ionic species in charged nanochannels

Cited by in corpus (4)

• Elevated temperature effects (T > 100 °C) on the interfacial water and microstructure swelling of Na-montmorillonite
• Complex coupling between surface charge and thermo-osmotic phenomena
• Slip-flow theory for thermo-osmosis based on a kinetic model with near-wall potential
• Electrical Response of Nanofluidic Systems Subjected to Viscosity Gradients